//弹出视频
var altsp = document.querySelector(".alt-sp");
var altmp4 = document.getElementById("alt-MP4");
//点击按钮的时候显示视频
altsp.onclick = function() {
	altmp4.style.display = "block";
}
//点击 差 关闭
altmp4.children[0].children[1].onclick =function() {
	altmp4.style.display = "none";
}